The invention relates to novel water soluble polymers, represented by formula (1), which are prepared by polymerizing vinylacetate and maleamic acid or its N-substituted derivatives in presence of a radical producing initiator, ##STR1## and to novel watersoluble polymers (2) being the hydrolysis-products thereof which are obtained by saponification of the acetate group. ##STR2## Said N-substituted maleamic acids are the reaction products of maleic anhydride with amines, aminocarboxylic acids, aminogroups--containing aromatic sulfonic acids and amino alcohols at a molar ratio of 1:1.
The invention also relates to the use of said polymers as dispersants and fluidizers for aqueous suspensions.
Dispersants have been commonly used as powerful waterreducers and fluidizers for high solids suspensions, and building or construction materials such as cement and cement mortar. Freshly prepared concrete, for example, is generally considered to be a mixture containing cement, mixing water and the aggregates sand and gravel of distinct particle size distribution. In contrast to concrete, a cement mortar contains no coarse aggregates, but often has a higher cement content.
After mixing, concrete passes several stages of development; i.e., from freshly prepared concrete to solid concrete. These stages may be partly influenced by particular additives.
Concrete additives are added to freshly prepared concrete and freshly prepared mortar and generally dissolved in the mixing water, in order to influence the workability and final characteristics thereof. Depending on the purpose of a building or construction part, as well as any other specific requirements, the characteristics of the concrete will have to be defined by the engineer. The most important characteristic with freshly prepared concrete are the workability, the inner cohesion and its consistency. In the case of solid concrete, the tensile and compressive strengths, resistance to frost, resistance to dew salt, waterproofness, resistance to abrasion and chemical durability are important.
All these characteristics are dependent on the water cement ratio. The water cement ratio: EQU w=W/C;
is obtained from the quantitative ratio of water (W) to cement (C) in freshly mixed concrete. With increasing water content the water cement ratio rises, and with increasing cement content it becomes smaller. A low water cement ratio affords better characteristics of the solid concrete and solid mortar.
On the other hand, a higher water cement ratio provides better workability of freshly prepared concrete. The transfer of freshly prepared concrete from a concrete mixer into the (concrete) form, and the subsequent solidification in the (concrete) form requires a considerable consumption of work and control of work. Therefore, considerable differences in cost may arise depending on the workability of a particular batch.
In order to reduce expenditure on work and cost, concrete mixtures have been made more liquid by adding more mixing water (which increases the water cement ratio). Unfortunately, this has always resulted in reduced strength for the hardened concrete. In recent years so-called fluidizers (also frequently referred to as super plasticizers or high range water reducers) have been increasingly used which allow for an improvement in the consistency of a concrete mixture at a constant water cement ratio.
Polycondensates such as the sodium or calcium salts of sulfonated naphthalene formaldehyde condensates described in U.S. Pat. No. 3,537,869, or salts of sulfonated melamine formaldehyde condensates such as those described in DE-PS 1 671 017, have been used as super plasticizers in order to improve the workability and the time dependent flow behaviour of cement mortars and concrete. These water reducing agents can improve the flowability of such mixtures, but this flowability may not be maintained according to normal practice for a sufficiently long period of time. As a result, additional amounts of water reducing agents have to be added at certain intervals.
Particularly in the transportation of ready mixed concrete, where long ways and delays are inevitable, supplemental dosages of superplasticizers are necessary. However, it is known from experience that only two additional dosages can be used with success and that more dosages are less effective or even may cause retardation of the development of strength.
Water reducing agents have also been used in the production of gypsum building materials such as gypsum board. Gypsum is the generic name for the mineral (hydrous calcium sulfate, CaSO.sub.4.2H.sub.2 O ) variously known as selenite, satin spar, alabaster, rock gypsum, gypsite, etc., and is commonly used to make a form of plaster.
In the production of gypsum sheet materials (e.g., gypsum board which is a gypsum plaster board covered with paper), sheet products are normally fabricated on a high speed machine that automatically spreads a foamy piaster core between sheets of tough surface papers, and cuts the resultant board to proper dimensions. In the past, water reducing agents have been added to plaster solutions to ease processing. These agents have commonly been formaldehyde containing water reducers.
Formaldehyde, unfortunately, is toxic (e.g., by inhalation) and its handling and containment constitutes a tremendous practical problem during the production of gypsum materials. For example, formaldehyde is released in the air when gypsum board is dried.
In order to avoid formaldehyde, other polymer types may be applied, which are synthesized e.g. by radicalic polymerization of ethylenic groups--containing hydrophilic monomers. It is generally known that maleic acid derivatives thereof may be radically copolymerized with an olefinic group containing monomer. Many of these products may be used as water-soluble polymeric dispersing agents. For example, U.S. Pat. No. 3,116,254 describes a copolymer of maleic acid and N-vinylpyrrolidinone and its use as a fluidizer, e.g. for hydraulic cement compositions, which, as compared to sulfonated naphthalene-formaldehyde,--and melamine formaldehyde--polycondenstates, imparts equal flowability and an even better workability. A similar effect is displayed by a copolymer of maleic acid with vinylacetate instead of N-vinylpyrrolidinone as a comonomer, which is described in Japan Patent No. 11,282 (1963). On the other hand, a copolymer of maleamic acid (maleic acid halfamide) and vinylacetate which is claimed in U.S. Pat. No. 3,554,287 shows an unexpected contrary effect on the flowability and causes thixotropy and early stiffening if admixed to fresh concrete samples. Similar copolymers of N-alkyl-substituted maleamic acids and vinylacetate exhibit a high surface tension which is increasing with growing chain length of the N-alkyl side groups. We have inventively found that copolymers which contain C.sub.1 -C.sub.4 -alkyl sidegroups can be used as dispersants for cement pastes and concrete to improve flowability and workability but with the disadvantage of an appreciable loss of final compressive strengths of the hardened building material.
In contrast to the copolymers mentioned above, the surface tension of aqueous media containing an inventive copolymer having a hydrophilic funtional group on the side chain is considerably lower. For that reason it was very surprising that the inventive copolymers impart an outstanding high flowability and an unexpected long lasting workability to concrete and that no appreciable retardation of initial setting and early strengths was observed.